外文翻译--微机电系统的未来（MEMS）

微机电系统的未来（ MEMS） Minhang Bao a, Weiyuan Wang b Fudan University, Shanghai. 200433 Chinab Shanghai Institute of Metallurgy. Shanghai. 200050 China 摘要 基于微加工和微电子技术微机电系统（ MEMS）的发展已经近十年显著。然而，这是不切实际的考虑微加工技术为传统加工的微型版本技术。由于事实上，微机械加工技术，硅的平面技术梗和基本上是一个二维加工技术。另一方面，很明显，一 个微机械不可以与常规的机械强度比较。对于 MEMS 在未来的成功发展，一个简单的规则，建议由获得了在过去数年的经验：尽量为了避免尽可能多的机械耦合与外部世界的同时努力提高 MEMS 技术提升该装置的机械功率。除此之外，被证明是正确的固态传感器的发展战略也适用： MEMS 器件应主要用于具有广阔的市场新开发的应用程序。其取代传统的应用程序不应该被视为发展的主要策略。根据这些参数， MEMS器件和技术的未来发展在本文中进一步讨论 . 1。 MEMS 的发展 在本期刊的早期问题的前盖 （传感器和执行器）有刚下的字幕 其内容主标题： “国际期刊致力于固态传感器的研究和发展”。这些平实的话语对我们意味着该杂志的创始人， 西蒙教授预见的出现固态驱动器，并且，因此，micivelecisome chaaical 系统（即， MEMS），从最后的一开始十年。 微机电系统是集成的系统，包括微电子 （ IC），微致动器，并且在大多数情况下，微传感器。 微电子技术得到了迅速发展自 1960 年以来，并已自 1970年代已经相当成熟。微技术，该技术为机械传感器和微执行器，一直在开发几乎处于随着微电子技术的平行，但前者已成熟远远落后。 在较早的阶段，微机械加工的发 展主要集中在体微机械加工主要是与相关固态压力传感器。人在当时都没有预计从微机械一体化太多结构和微电子因为批量 MEMS 技术以及固态压力传感器相对难以与微电子集成 . 在 1987，第一可动微机械部件是通过表面微机械加工技术制造的和典型的微致动器，静电微电机，是成功在明年操作。由于高表面微加工和之间的兼容性微电子技术之间的融合微机械和微电子导致的诞生 MEMS 在随后的岁月。 由于出现了微机电系统没有明确的定义，在此文章中，我们考虑一个典型的 MEMS 器件为： （ 1）一种设备，包括一个微机械和微电子，其中微型机械是由控 制微电子。很多时候，微传感器参与控制系统通过对微电子提供的信号。 （ 2）正在使用微加工的设备技术与 IC 工艺，即。技术批制造。 （ 3）设备有一个完整出生的，没有个人装配步骤的设备的主要部分以外的包装所需的步骤 . 这些点表示的压力传感器不被认为是作为一个典型的 MEMS 装置，但作为一个机械传感器，因为没有 MEMS 控制微机械结构。另一方面，微型电机不是典型 MEMS 器件，但一个典型的一部分微致动器。由于 MEMS 是微机械加工技术的集成和微电子（集成电路）技术，它们出现后不久，微机械在 1987 年问世。发展 MEMS 的几 乎一个十年已经显著： 各种新技术已经发展，许多新的器件的设计，并与其中的一些制备被商业化，并在微机电系统的研究已进行几乎所有主要的大学和研究机构 ,从行业及政府享有广泛的支持机构。该字段已被描述为“生长成 从不确定的公信力，动态和流行的青春期在不到十年的孩子 . 但每一线希望有云，这种情况下是没有例外。在快速发展而发展的几个问题。新的微型机器的外观迅速激起了很高的期望从科学界甚至公众的新闻媒体。有的倾向于认为，最复杂的机电系统，就像一个机器人，可以被复制到一个微版和微机械罐还是做了类似的工作，以宏观的同行。有 一直离谱的预测，像微型机器人收集了放射性粒子在有毒场所，和 MEMS 跟踪和攻击病毒和癌细胞，而通过游泳。上实发展很难匹配从新闻这样的发展模式媒体。虽然微电机的设计和制造一个接一个，他们遇到的小的通病扭矩和相对较大的摩擦在微米尺度。人通常由微型马达的运转激发简单地说，不能够期望过高的条款， F 的扭矩 /功率输出。这似乎不切实际的把它们投入使用像传统的机器。到目前为止，还没有微机械可代替在任何实际应用传统的机器。这情况已经引起了怀疑过云的未来微机电系统 . 然而，应用程序始终是最终的驱动力任何新兴技术。起始于今年年初 十年中，微致动器的实用应用已经谈到越来越多的时候通过换能器社区并已使越来越多的努力，把微执行到实际应用中。 已经有两种方法，到目前为止，推动应用微致动器。方法之一是让它更强大。例如，通过双金属结构所产生的力是够大对于许多应用，例如打开和关闭微型阀。这项计划相当成功，使得微型阀已经商业化。形状记忆合金（ SMA）也能产生很大的力，并已考虑用于类似的目的。对于微型马达，电磁电机的设计与制造。该扭矩可以是若干个数量级比静电微电机的高一些，但仍然有相当多的有关的设计和加工问题 . 另一种方法是寻找一些新的应用其中一点力 输出是必需的。要做到这一点，直接微型机械与机械之间的耦合应避免宏观世界。之间的界面 MEMS 与外界将通过电学，光学和磁信号。这种方法导致了相当很多 MEMS 与实际应用的设备他们中的一些已经商业化。这次成功的经验告诉我们， MEMS 的未来是光明的，如果微机械加工技术的本质是尊重。 2。微加工技术的性质 微机电系统是两个现代技术的后代中，微电子和微机械加工技术。从的技术观点来看，也有一些亲和性这两种技术之间。它是众所周知，微电子从平面技术（集成电路）技术的梗硅。作为事实上的，平面的应用硅的机械结构的形成过程催生了微 加工技术。平面技术的固态成功应用压力传感器促进微细加工的发展在早期阶段 . 基本上，有微细加工的两个主要类别技巧：批量微加工和表面微加工。该技术被称为体微机械加工当基片的散装材料（一般的硅）参与的过程，就好像表面微加工的表面上只沉积（或镀）膜基板都参与了加工过程。这两种类型的的微加工技术具有相同的美德微电子技术，也就是说，精度高，批量制造，但它们都具有相同的限制，从而产生平面加工技术 . 首先，结构由微机械技术可以是在外观，但它们是两个维本质，因为它们是按照一定的演变规则从平面蚀刻掩模。该结构可以是变得更加复杂 ，重复成膜和掩蔽刻蚀不止一次，但柔韧性仍限制重复的数目和处理顺序从衬底的表面开始。因此，它是不切实际的考虑微加工技术作为微版本的常规加工技术，因为它有平面工艺的局限性：一个基本上二维加工技术不适合于装配步骤来构造一台机器从逐张 ； 。双重加工零件。我们不能指望微机械加工技术是一样灵活和通用的如在传统的常规机械加工世界。一些选择性沉积和蚀刻技术声称有真实的三维功能正在开发中，但它仍然是太早雷斯。他们在实践中可能的应用 . 因此，一个简单的规则必须是九，我在心里由传统的机械制造所有的机械结构在微机械技术的版本无法复 制他，和大型数组，结构简单，比较适合用于微机械加工技术比一台机器复杂的结构。 另一方面，很明显，一个微型机械能很难用常规的机械强度比较和电源。较小的结构，较小的强度和功率输出，它可以提供。在许多情况下，微型机器甚至在刚刚常规运行困难 环境由于在微观尺度超大摩擦和灰尘，湿度等的干扰，更不用说上的功率输出以驱动 macromachine. 对于 MEMS，多了一个简单的开发成功规则建议：尽量避免尽可能多的机械 动力输出的同时努力提高 MEMS 技术以提高机械强度和功率设备。 重要的是要尊重的一种新技术的本质是很重要的 使其潜能得以充分发挥。由于事实上，有在短期内已经有许多成功的经验微机电系统的充分利用的优势和历史避免了微机械加工技术的缺点。 3。 MEMS 器件的未来 正如上面提到的，对于 MEMS 的未来发展技术，应使两方面的努力：一种是不断提高微细加工技术和二是制定实际应用适当的设备据中的 MEMS 技术的本质化。该后者是当前的一项紧迫任务，第一件事我们要解决的是：什么是适当的 MEMS 器件？ 作为微加工技术具有的优点高精度低成本的批量生产，但局限性二维掩蔽，低强度，低功率输出和高敏感性的许多环境的干扰因素，例如灰尘，湿度等，未 来的 MEMS 设备应主要是打包独立的子系统由微型机械 microelectrouics，并且在许多的情况下，微传感器。 MEMS 结构之间的耦合设备与外界将主要是通过电，电源光，磁等非接触式信号供应，浓度 XOL 信息，输入和输出信号。一大阵相对简单的机械结构是优选复杂的机械结构 此外，未来的 MEMS 器件应着眼于新的应用具有广阔的市场，使该设备可批量生产，充分发掘平面工艺的优势在低成本的大规模生产。这里所提出的论点西蒙Middelhoek 教授硅智能传感器适用于 MEMS 太：在替代旧的应用程序没有创建一个足够大的市场潜 力。因此， 它不能被认为是未来的一个主要策略微机电系统的发展。 由于事实上，在上述提到方法有被证明是成功开发的 MEMS 器件过去和将被改编为将来发育。各种满足上述标准的 MEMS 器件将在将来开发的，并在下面描述的弧，对于惯性传感 MF.MS 设备 。 在硅加速度计发展迅速过去十年中，且被视为下一 massproduced 硅后微机械传感器。最吸引人型微加速度时，加速度计，实际上是在一个 MEMS 器件组成光束质量的机械结构，一个电容性传感器用于质量块的位置，所述信号处理电子设备为传感器和静电致动器施加一个反馈强制地震质量。 各种力量平衡microaccelerometers 已经发展到现在，但至今其中最成功的是完全集成的微加速度， ADXLSO，这是发布了关于生叶芝前。 该装置的机械结构是通过制作装置的多晶硅表面微加工，以及电子通过的BiCMOS IC 技术手段制作。针对安全气囊释放控制，操作应用程序该设备的范围 50 克与 5 V 单电源供电。 整个微系统是制作在硅芯片上测量的 3 mm 3mm，且采用 TO-I00 可以。虽然过程被认为是相当复杂和困难的 9，开发者声称，他们可以在成本销售根据 15 美元每人。此外，改进的版本操作范围低至 5 克或 LG已经公布。基于 SIMOX SOI 材料类似的设备厚外延多晶硅也被开发。 力平衡 microaccelerometers 可以被视为其中最成功的 MEMS 目前的。一个原因他们的成功是由地震感知加速度质谱是通过非接触式的惯性力和输出是一个电信号，使整个系统可以是气密在一个包，保证了密封的性能的微机械结构不会受到任何阻碍环境干扰。第二个原因是，加速度计可以找到大量的应用在各种motioncontrol 的系统。一个明显的例子是大规模应用 在汽车安全气囊控制。这种应用从产业带动显著的兴趣和投资 另一个惯性检测装置，陀螺仪 ，也有类似的操作模式的加速度，也可以找到广泛应用在运动控制，包括汽车应用，如牵引力控制系统和行驶稳系统，消费电子应用，如摄像机稳定和航模稳定计算机应用，例如惯性鼠标，机器人应用，当然，军事应用。因此，微机械陀螺仪已接收旺盛在近几年的发展努力 作为高速旋转的零件，轴承在一个传统的陀螺仪是很难小型化和批量制造 ,通过微机械技术生产低成本器件，微机械陀螺仪是专门振动类型，包括双万向支架结构，悬臂梁结构，音叉结构和振动环结构。其中的振环装置是最先进的，这是开发由 LIGA-iike后电路工艺结合比电铸金属的微观结构与 CMOS电路用于控制和读出电子。 虽然没有这些微机械陀螺仪的有已经商业化的是，这是很可能的是某种形式的 MEMS 陀螺仪将被大规模生产，在不久的将来。 参考文献 1 S. 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Sygiyama ， Electrostat ， c 用溶胶晶圆，技术驱动的光学斩波器。文摘，第 7 诠释。机密。固态传感器和执行器（传感器 93 ） ，日本横滨， 6 月 7-10 日， 1993 年，第 124 - 127 。 20 E.许默和奥伯迈尔。 J. Lin 和五 Schkuchting 。设计的和制造 electrostatistically 驱动的微快门技术。文摘，第 7 诠释。机密。固态传感器和执行器（传感器 93 ） ，横滨，日本。 7 - 10June ， 1993 。页 132-135 。 21 S.T.威尔金森， Y.W.金， M.G.艾伦和 N.M. Jokerst ，整合薄膜化合物半导体光子器件的上微机械移动平台，技术。文摘，第 7 诠释。机密。固国家传感器和执行器（传感器 93 ） 。横滨，日本， 7 - 10June ， 1993 年，第 148-151 页。 221 J.莫尔， M.科尔和 W门斯，通过微型光开关静电线性致动器与大位移，技术。文摘，第七诠释。机密。固态传感器和执行器（传感器 93 ） ，日本横滨， 7 10June ， 1993 ，页 120-123 。 23 升 C.H.安贞焕， Y.J.金正日和 MG 。艾伦，完全集成的微加工环形电感与磁芯技术的镍 - 铁。文摘，第七诠释。机密。固态传感器和执行器 fTransducers 93 ） ，日本横滨。 7-10 1993 年 6 月，页 70-73 。 24 S. Kawahito ， Y. 佐佐木，石田米和 T 村，一个磁通门与微机械电磁阀和电镀磁传感器pennalloy 核心，技术。文摘，第 7 诠释。机密。固态传感器和执行器（传感器 93 ） ，日本横滨， 7 10June ， 1993 年，页。 888-891 。 25楼 Catdot ， J. Gohet ， M. Boganski 和 F 鲁道夫的微细加工微型电磁铁 tdgh 密度阵列wlth 片上电子，技术。文摘，第 7 整型。机密。固态传感器和执行器（换能器“ 93 ） ， Yokohamo 。日本， 7 10June ， 1993 ，页 32-35 。 26 W.汤，五 Temesvary ，林俊杰。 YBO ， Y.C. Tat 和 D.K.妙，硅微致动器用于计算机磁盘驱动器，在日本学者 Appl 。物理学报， 35 （ 1996） 50-356 。 27四妙和 Y.C.大，缩放技术： 10 GB / 2 。研讨会上微机电系统。 Taipai 。 Tmwan 。 3月 21 日至 24 日。 1994 页。 36 。 Future of microelectromechanical systems (MEMS) Minhang Bao a, Weiyuan Wang b Fudan University, Shanghai. 200433 China b Shanghai Institute of Metallurgy. Shanghai. 200050 China Abstract The development of microelectromechanical systems (MEMS) based on micromachining and microelectronics technologies has been significant for almost a decade. However, it is unrealistic to consider micromachining technology as a micro version of conventional machining technology. As a matter of fact, micromachining technology stemmed from the planar technology of silicon and is basically a two.dimensional processing technology. On the other hand, it is obvious that a micromachine cannot compare with a conventional machine in strength and power. For the successful development of MEMS in the future, a simple rule is suggested by the experience gained in the past few years: try to avoid as much as possible mechanical coupling with the outside world while trying hard to improve the MEMS technology to enhance the mechanical power of the devices. In addition to that, the strategy proven to be correct for the development of solid-state sensors also applies: MEMS devices should mainly be developed for new applications with a vast market. Their substitution for traditional applications should not be considered as a main strategy of development. Based on these arguments, the future development of MEMS devices and technologies is further discussed in the paper. 1. The development of MEMS On the front cover of the earlier issues of this journal (Sensors and Actuators) there was a subtitle just under the main title which read: international journal devoted to the research and development of solid-state transducers 1. These plain words mean to us that the founder of the journal, Professor Simon Middelhoek, foresaw the emergence of solid-state actuators, and, therefore, micivelecisome, chaaical systems (i.e., MEMS), from the very beginning of the last decade. MEMS are integrated systems consisting of microelectronics (IC), microactuators and, in most cases, microsensors. Microelectronics technology has been developing rapidly since 1960 and has been quite mature since the 1970s. Micromachining technology, the technology for mechanical sensors and microactuators, has been developing almost in parallel with microelectronics technology, though the former has lagged far behind in sophistication. At an earlier stage, the development of micromachining was focused on bulk micromachining mainly associated with solid-state pressure transducers. People at the time did not expect too much from the integration of micromechanical structures and microelectronics because bulk-micromachin-ing technology as well as solid-state pressure transducers were relatively difficult to integrate with microelectronics. In 1987, the first movable micromechanical parts were fabricated by surface-micromachining technology 2 and a typical microactuator, the electrostatic micromotor, was successfully operating in the next year 3. Due to the high compatibility between the surface micromachining and microelectronics technologies, the integration between micromachines and microelectronics led to the birth of MEMS in the following years. As there has been no clear definition of MEMS, in this article we consider a typical MEMS device as: (1) A device that consists of a micromachine and microelectronics, where the micromachines are controlled by microelectronics. Quite often, microsensors are involved in the control system by providing signals to the microelectronics. (2) A device that is fabricated using micromachining technology and an IC process, i.e. technologies of batch fabrication. (3) A device that is integratedly born, without individual assembly steps for the main parts of the device except for the steps required for packaging. These points mean that a pressure transducer is not considered as a typical MEMS device but as a mechanical sensor as there is no microclectronics control over micromechanical structures. On the other hand, a micromotor is not a typical MEMS device but a typical part ofMEMS D a microactuator. As MEMS are an integration of micromachining technology and microelectronics (IC) technology, they emerged soon after the advent of the micromachine in 1987. The development of MEMS for almost one decade has been significant: various new techniques have been developed, numerous new devices have been designed and fabricated with some of them being commercialized, and research on MEMS has been conducted by almost all major universities and research institutions, enjoying wide support from industries and government agencies. The field has been described as growing into a credible, dynamic and popular adolescence from an uncertain child in less than a decade 4. But every silver lining has a cloud, and this case was no exception. Some problems developed during the rapid development too. The rapid appearance of new micromachines stirred up high expectations from the scientific communities and even public news media. Some tended to believe that the most sophisticated electromechanical system, like a robot, can be copied into a micro version and the micromachine can still do a similar job to its macro counterparts. There have aoo been outrageous predictions, like microrobots gathering up radioactive particles at toxic sites, and microsubmarines stalking and attacking viruses and cancerous cells while swimming through the bloodsueam. The real development can hardly match such a development pattern from the news media. Though micromotors have been designed and fabricated one by one, they run into the common problem of small torque and relatively large friction on the micron scale. People are usually excited simply by the functioning of a micromotor, not being able to expect too much in terms ,:f torque/ power output. It seems impractical to put them into use like a conventional machine. So far no micromachine can replace a conventional machine in any practical application. This situation has given rise to a sceptical cloud over the future of MEMS. However, application is always the final driving force for any emerging technology. Starting at the beginning of this decade, the practicai application of a microactuator has been talked about more and more often by the transducer community and more and more efforts have been made to put microactuators into real application. There have been two approaches so far to push forward the application of microactuators. One of the approaches is to make laicroactuators more powerful and stronger. For example, the force produced by a bimetal structure is large enough for many applications, such as to open and close microvalves. This scheme has been quite successful so that the electrocontrolled microvalve has been commercialized. Shape memory alloy (SMA) can also produce a large force and has been considered for similar purposes. For micromotors, electromagnetic motors have been designed and fabricated. The torque can be several orders of magnitude higher than that of an electrostatic micromotor, but there are still quite a lot of problems related to the design and processing. Another approach is to look for some new applications where little force output is required. To do this, direct mechanical coupling between the micromachine and the macro world should be avoided. The interface between the MEMS and the outside world will be through electrical, optical and magnetic signals. This approach has resulted in quite a lot MEMS devices with practical applications； some of them has been commercialized. This successful experience tell us that the future of MEMS is bright if the nature of micromachining technology is respected. 2. The nature of micromachining technology MEMS are the offspring of two modern technologies, the microelectronics and the micromachining technologies. From a technological point of view, there are some affinities between these two technologies. It is well known that microelectronics (IC) technology stemmed from the planar technology of silicon. As a matter of fact, the application of planar processes of silicon to the formation of mechanical structures gave birth to micromachining technology in the 19/0s. The successful application of planar technology in solid-state pressure transducers promoted the development of micromachining at the early stage. Basically, there are two main categories of micromachining techniques: bulk micromachining and surface micromachining. The techniques are called bulk micromachining when the bulk material of the substrate (in general silicon) is involved in the process and as surface micromachining if only the deposited (or plated) films on the surface of the substrate are involved in the machining process. Both types of micromachining technologies have the same virtues as microelectronics technology, i.e., high precision and batch fabrication, but they have the same limitations stemming from planar processing technology. First, the structures made by micromechanical technology can be three dinensional in appearance, but they are two dimensional in essence as they are evolved according to certain rules from planar etching masks. The structures can be made more complicated by repeating the film deposition and masked etching more than once, but the flexibility is still limited by the number of repititions and the processing order starting from the surface of the substrate. Therefore, it is unrealistic to consider micromachining technology as a micro version of conventional machining technology as it has the limitation of the planar process: a basically two-dimensional processing technology not suitable for assembly steps to construct a machine from indiv；.dually processed parts. We cannot expect micromachining technology to be as flexible and versatile as conventional machining in the conventional world. Some selective deposition and etching techniques claimed to have real three-dimensional capability are under. development 5,6, but it is still too early to fores.e their possible application in practice. Therefore, one simple rule that has to be Ix)me in mind is that all mechanical structures made by conventional mechanical technology cannot he copied in micromechanical versions, and large arrays with simple structure are more suitable for micromachining technology than a single machine with complicated structure. On the other hand, it is obvious that a micromachine can hardly compare with a conventional machine in strength and power. The smaller the structure, the smaller the strength and the power output it can provide. In many cases, micromachines even have difficulties in just running in a conventional environment due to the extra-large friction on the micro scale and the interference of dust, humidity, etc., not to mention on the power output to drive a macromachine. For successful development of MEMS, one more simple rule is suggested: try to avoid as much as possible mechanical power output while trying hard to improve the MEMS technology to enhance the mechanical strength and power of the devices. It is important to respect the nature of a new technology so that its potential can be fully explored. As a matter of fact, there have been many successful experiences in the short history of MEMS by making full use of the advantages and avoiding the disadvantages of micromachining technology. 3. The future of MEMS devices As mentioned above, for the future development of MEMS technology, two-fold efforts should be made: one is to improve micromachining technologies continuously and the other is to develop appropriate devices for practical applition according to the nature of the MEMS technologies. The latter is an urgent task at present, lherefore, the first thing we have to address is: what are the appropriate MEMS devices.? As micromachining technologies have the advantage of high-precision low-cost batch production but the limitations of two-dimensional masking, low strength, low power output and high susceptibility to the interference of many environment factors, such as dust, humidity, etc., the future MEMS devices should be mainly packaged independent subsystems consisting of micromachines microelectrouics and, in many cases, microsensors. The coupling between the MEMS devices and the outside world would mainly be via electrical, optical, magnetic and other non-contact signals for power supplies, conxol information, input and output signals. A large array of relatively simple mechanical structures is preferable to complicated mechanical structures. Also, the future MEMS devices should be aimed at new applications with a vast market so that the device can be mass produced to explore fully the advantage of a planar process in low-cost mass production. Here the argument made by Professor Simon Middelhoek 7 for silicon smart sensors applies to MEMS too: substitution in an old application does not have the potential to create a large enough market. Therefore, it cannot be considered as a main strategy for future MEMS development. As a matter of fact, the above-mentionod approaches have been proven successful in developing MEMS devices in the past and will be adapted for future devel)pment. A variety of MEMS devices meeting the above-mentioned criteria will be developed in the future, and arc described below. 3. MF.MS devices for inertial sensing Silicon accelerometers have been developing rapidly during the last decade and are considered as the next massproduced micromechanical sensor after silicon pressmsensors. The most attractive type of microaccelerometer, the fort.ebalanced accelemmeter, is in fact a MEMS device consisting of a beam-mass mechanical structure, a capacitive sensor for the position of the mass, the signal-processing electronics for the sensor and an electrostatic actuator to apply a feedback force to the seismic mass. A variety of force-balanced microaccelerometers have been developed by now, but so far the most successful one is the fully integrated microaccelerometer, ADXLSO, which was released for production about two yeats ago 8. The mechanical structure of the devices is fabricated by means of polysilicon surface micromachining, and the electronics are fabricated by means of BiCMOS IC technology. Aiming at applications for airbag release control, the operation range of the device is 50g with a single 5 V power supply. The entire microsystem is fabricated on a silicon chip measuring 3 mm 3 mm and housed in a TO- I00 can. Though the process is considered quite sophisticated and difficult 9, the developer claimed that they can be marketed at a cost under US$15 apiece. Furthermore, an improved version with an operation range as low as 5g or lg has been announced 10. Similar devices based on SIMOX SOI material 11 and thick epi-polysilicon have also been developed 12. Force-balanced microaccelerometers can be considered as one of the most successful MEMS at present. One reason for their success is that the sensing of acceleration by the seismic mass is through non-contact inertial force and the output is an electrical signal so that the whole system can be hermetically sealed in a package to ensure that the performance of the micromechanical structures would not be hindered by any environmental interferences. The second reason is that accelerometers can find mass application in a variety of motioncontrol systems. A notable example is for mass applications in airbag control in automobiles. This kind of application spurred significant interest and investment from industry. Another inertial sensing device, the gyroscope, has a similar operation pattern to the accelerometer and can also find wide applications in motion control, including automotive applications such as traction control systems and ride-stabilization systems, consumer electronics applications such as video camera stabilization and model aircraft stabilization, computer applications such as an inertial mouse, robotics applications and, of course, military applications. Therefore, the micromechanical gyroscope has been receiving vigorous development efforts in recent years. As the high-speed rotation parts and bearings in a traditional gyroscope are difficult to miniaturize and batch fabricate by micromechanical technologies to produce low-cost devices, micromechanical gyroscopes are exclusively of vibrating types, including double-gimbals structure 13, cantilever beam structure 141, tuning-fork structure 15 and vibrating ring structure 16. Among them the vibrating ring device is the most sophisticated one, which is developed by a LIGA-iike post-circuit process for incorporating highaspect- ratio electroformed metal microstructures with a CMOS circuit for control and readout electronics. Though none of these micromechanical gyroscopes has been commercialized yet, it is quite likely that some form of MEMS gyroscope will be mass produced in the near future. References 1 S. Middelhoek, Sensors and Actuators. ! ( 1981 ) front cover. 2 L.S. Fan, Y.C. Tai and R.S. Muller, Integrated movable micromechanical structure for sensors and actuators, IEEE Trans. Electron Devices. 35 (1988) 724-730. 3l L.S. Fan, Y.C. Tai and R.S. Muller, IC-processed electrostatic micromotor, Proc. 1988 IEEE int. Electron Devices Meeting, San Francisco, CA, USA, !1-14 Dec. 1988. pp. 666-669. 4 K. Petersen, MIEMS: What lies ahead, Tech. Digest, 8th Int. Conf. Solid.State Sensors and ActuatorslEurosensors IX, Stockholm. Sweden. 25-29.；une, 1995, Vol. 1, pp. 894-897. 5 T.M. Bloomestein and D.J. Ehrlich, Laser deposition and etching of three-dimensional microstructuw, Tech. Digest, 6th Int. Conf. Solid- State Sensors and Actuators (Transducers 91), San Francisco. CA, USA, 24-28June, 1991, pp. 507-511. 6 H. Westberg, M. Boman, S. Johansson and J. Schweitz, Truly three dimensional structures microfabricated by laser chemical process, Tech. Digest, 6th Int. Conf. Solid.State Sensors and Actuators (Transducers 91), San Francisco, CA, USA, 24-28 June, 1991, pp. 516-519. 7 S. Middelhoek, Seminar at Shanghai Institute of Metallurgy. Chinese Sciences Academy, October 1995. 8 W. Kuehnel and S. Sherman, A surface micromaehined silicon acceleromeler with on-chip detection circuitry, Sensors and Actuators A, 45 (1994) 7-16. 9l T.A. Core, W.K. Tsang and SJ. Sherman. Fabrication technology for an integrated surface micromachined sensor. Solid State Technol., :Oct.) (1993) 39. 10 K.H.L. Chart. S.R. Lewis. Y. Zhao, R.T. Howe, S.F. Ban and R.G. Marcheselli, An integrated force-balanced capacitive accelemmeter for Iow-g application. Sensors and Actuators A, 52-54 (1996) 472-476. 11 L. Zimrnermann et at., Airbag application: a microsystem including a silicon capacitive acceleromeer, CMOS switched capacitor electronics and true self-test capabi.*!ly, sensors and Actuators A. 46-47 (1995) 190-195. 12 M. Offenherg, F. I.,arnr, B. Eisner, H. Munzel and W. Riethmuller, Novel process for monolithic integrated accelerometer, Tech, Digest, 8th int. Conf. Solid-State Sensors and Actuators/Eurosensors IX, Stockholm, Sweden, 25-29 June, 1995, Vol. 1, pp. 589-592. 13 P. Greiff, B. Boxenhom, T. King and L. Nilus, Silicon monolithic micromechanical gyroscope, Tech. Digest. 6th Int. Conf. Solid-State Sensors and Actuators (Transducers 91)